On the app there is a slider just to the right of the equaliser display, and above the icons for Favorites, Volume, Tools etc. - see attached fileI have not been able to determine exactly what it is.Can anyone help me out?

It is the volume-slider. I am sure you did try it (grab with the mouse and move it , and hear the difference in soundvolume...)To be honest, for someone who can make screenshots, can edit them with a graphical program, and post all here, I cannot believe this question is real ...... (there must be an other reason for posting, my opinion)

I had been recording a radio station using a laptop, but with the volume on the laptop muted, and actually listening to it via a phone app. Hence, moving the slider on the laptop had no apparent effect..Silly me. All sorted now, thanks.